Electrical measuring instrument.



No. 644,9l7. Patentedlar, 6, I900.

' A. H.,'HOYT.

ELECTRICAL MEASURING-INSTRUMENT.

. (Application filed Sept. 22, 1899.) (No Model.)

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Nrrn TATES ADRIAN II. IIOYT, OF PENAOOOK, NEW HAMPSHIRE.

ELECTRICAL M EASURING INSTRUM ENT.

SPECIFICATION forming part of Letters Patent No. 644,917, dated March 6,1900.

Application filed September 22, 1899. Serial No. 731,248, (No d m T aZZwhom it may concern.-

Be it known that I, ADRIAN H. How, a citizen of the United States,residing at Penacook, in the county of Merrimac and State of NewHampshire, have invented certain new and useful Improvements inMeasuring Instruments, of which the following is a full, clear, andexact specification.

My invention relates to electrical measur- 1o ing instruments; and itsobject is to construct an instrument which shall be simple andeconomical in construction and shall be highly sensitive to variationsof current values in the current to be measured.

A further object to be attained by the invention is to provide means forconveying the actuating-current to the coil without interfering with themechanical operation of the instrument.

The invention is applicable alike to either voltmeters or ammeters.

In carrying out my invention I propose to employ a movablecoil actuatedby the current to be measured and movable through a field of forcebetween the polesof a permanent or electro magnet, the extent ofmovement depending upon the voltage or amperage of theactuating-current, and to provide means for concentrating the lines offorce in 0 the field into a relatively-small space and limit themovement of the coil to this space. To obtain any desired range ofmovement of the indicating-needle upon the scale I employsuitablemultiplying devices between the movable coil and the needle.

In instruments heretofore in general use it has been customary to conveythe current to the coil through the springs employed to oppose themovcment of the coil. This is ob- 0 jectionable in that in order toavoid the heating of the spring which follows, forcing acomparatively-heavy current through a light spring, it has been foundnecessary to increase the size of the spring considerably beyond thesize which would normally perform the retarding or opposing work. Itherefore propose to provide independent flexible conductors of lowresistance for conveying the current to the coil, and thus be enabledto5c utilize springs of lightconstruction to perform the opposing work.

The invention comprehends various fea-- tures of advantage which willmore clearly appear hereinafter, and it will be more par ticularlydescribed with reference to the form 5 5 thereof illustrated in theaccompanying drawings, in which- Figure 1 is a perspective view of ameasun ing instrument embodying the principles of my invention. Fig. 2is a detail sectional view of the coil and surrounding parts, and Fig. 3is a detail sectional view illustrating the manner of conveying thecurrent to the coil.

Referring more particularly to the drawings, 1 represents a magnetemployed to produce the field of force through which the coil is to bemoved. In this instance the magnet employed is a permanent magnet, butif preferred it may be an electromagnet. The poles 2 and 3 of the magnetare provided with tapered ends facing each other and leaving a smallair-gap between the same. The end of pole 2 is provided with a convexsurface 4', and the pole 3 with a concave surface 5, thus 7 providing asegmental-shaped air-gap between the poles. The length of the airgapwill be adjusted according to the conditions of size of the instrumentand work upon which it is to be used; but to produce best results oughtto be relatively short in comparison with the width of the polepieces,whereby the lines of force passing from one pole-piece to the other willbe concentrated into this short air-gap. The pole-piece 2"is providedwith a suitable opening 6, through which a suitable shaft 7 extends, theshaft having its bearings in suitable supports 8. Upon the shaft 7 ismounted the coil 9, the latter surrounding the pole-piece 2, as illus-9o trated in the drawings, and having one side extending through theair-gap between the poles 2 and 3, the coil being adapted to swing uponthe shaft 7, its side 10 thereupon moving through the path of theair-gap. The 5 coil 9 is made up of wire of suitable fineness andconductivity to adapt the instrument for the use to which it is to beput and will be connected in series with or shunt to-the source ofcurrent to be measured, according to which I oo acts as a counterbalanceto evenly balance the coil on its shaft. In practice the extension willgenerally carry an adjustable Weight In a suitable bearing 12 is mountedan axis 13, to one end of which is fixed the indicating-needle 14, whichis arranged to swing so that its pointer will move from end to end ofthe calibrated scale 15. Upon the axis 13 is mounted a roll or cam 16,to whichis attached one end of a thin cord 17 or other flexibleconnection, the other end of the cord being attached to the coil 9.Suitable slots 18 are cut in the pole-pieces 2 and 3 to permit the cord17 to move freely. Asuitable spring or springs 19 is arranged upon theaxis 13 to oppose the movement of the coil under the influence of themagnet. The terminals 19 and 20 of the current to be measured passthrough the pole-piece 2 into the opening 6, being suitablyinsulatedfrom the pole-piece,

- one of the terminals being located at or near one end of the opening 6and the other terminal being located at or near the other end thereof,substantially as illustrated in Fig. 3. From the terminals 19 and 20suitably-arranged flexible wires or strips 21 and 22 of conductingmaterial of low resistance respectively extend to the opposite sides ofthe coil 9, where they are connected to the terminals of the coil.

In operation the lines of force of the magnet between poles 2 and 3will,as before explained, be concentrated into the short air-gap, andwhen no current is flowing through the coil 9 the spring 19 will tend tohold the needle in zero position and, through the connection 17, willdraw the coil into the position shown in the drawings. When current isintroduced into the coil, a force is exerted, according to well-knownprinciples, tending to move the side 10 through the path of the air-gap,swinging the coil upon the shaft '7. By reason of the concentration ofthe lines of force the action of the coil when current is passed throughthe same will be more positive than has heretofore been the case. Withthe increase of current in the coil the force exerted at the-n1agnet-poles to move the coil is increased,

and the side 10 of the coil moves in opposition to the spring and drawsupon the connection 17, which swings'the needle upon its axis. The ratioof the movement of the needle with respect to that of the coil may beregulated by varying the size of the roll 16 and will of course varyaccording to conditions.

It will be observed that current at no time passes through the spring orsprings 19, and therefore the efficiency of the spring will not be inany wise impaired. Furthermore, when the coil swings upon its shaft theconductors 21 and 22 are moved but slightly from their positions and byreason of their flexibility will readily conform to whatever slightchange may occur.

Having thus described my invention, I declare that What I claim as new,and desire to secure by Letters Patent, is-

1. In a measuring instrument, the combination of a magnet having taperedpole-pieces, the ends of which face each other, a movable coil havingone side adapted to move between said tapered poles, anindicating-needle, and a connection between said coil and saidindicating-needle, substantially as described.

2. In a measuring instrument, the combination of a magnet having taperedpole-pieces the ends of which face each other, the surface of one ofsaid poles being convex and the other being concave a coil pivoted atone side and having its other side adapted to move between said taperedpole-pieces, an indicating-needle and a connection between said coil andsaid indicating-needle, substantially as described.

3. In a measuring instrument, the combination of a magnethavin gpole-pieces tapered toward each other,the ends of said. pole-pieceshaving oppositely-disposed convex and concave surfaces respectively, anopening in said convex pole-piece, a coil having one side pivotallymounted in said opening and surrounding said convex pole-piece, theother side of the coil being adapted to move between said pole-pieces,an indicating-needle, and a con nection between said coil andsaidindicatingneedle, substantially as described.

at. In an indicating instrument, the combination of amagnethavingtapered pole-pieces facing each other, the surface of one of said polesbeing convex and the other being concave, a coil pivoted at one side andhaving its other side adapted to move between said poles, apivotally-mounted indicating-needle, and a multiplying connectionbetween said coil and said indicating-needle, substantially asdescribed.

5. In an indicating instrument, the combi= nation of a magnet havingtapered pole-pieces facing each other, the surface of the end of one ofsaid poles being convex and the end of the other being concave, a coilpivoted at 'one side and having its other side adapted to move betweensaid poles, a pivotally-mounted indicating-needle, a roll fixedlyconnected with the bearing of said needle, and a flexible connectionbetween the periphery of said roll and the swinging end of said coil,substan-- tially as described.

0. In an indicating instrument, the combi-' .nation with the magnet, ofa pivotally-mounted coil, fixed terminals located adjacent to the pivotof said coil, terminals of said coil carried thereby and located at therespective ends thereof adjacent to the pivots, and fiexi ble conductorsconnecting each of said fixed terminals with one of the coil-terminals,said conductors extending directly between the respective terminals in asubstantially-straight line, substantially as described.

7. In. an indicating instrument, the combination with the magnets, of apivotally-mounted coil, fixed terminals located adjacent to the pivotsof said coil, terminals of said coil carried thereby and locatedadjacent to the respective ends thereof, and flexible conductorsconnecting said fixed terminals with the coilterminals, each of" saidconductors leading from its fixed terminal at one side of the shaft tothe coil-terminal located at the opposite end of the shaft, theconductors being substantially parallel to the shaft of said coil,substantially as described.

8. In an electrical measuring instrument, the combination of ashaftinfixed bearing, a coil having one side fixedly mounted on said shaft, itsotherside being free to rotate about said shaft as an axis, a field offorce influencing said moving side of the coil, an indieating-needle,aconnection between said nee- CID In testimony whereof I affix mysignature in presence of two Witnesses.

ADRIAN H. HOYT.

Witnesses:

DAVID F. DUDLEY, BLANOHE L. DUDLEY.

